The crew of the International Space Station (ISS) is preparing for an emergency spacewalk as early as tomorrow to fix an ammonia leak from the cooling system.

Commander Chris Hadfield reported seeing small white flakes floating away from the P6 truss structure of the ISS last night. Mission Control confirmed that the ammonia used to cool the station's power channels, which provide electricity to all of its systems, was escaping and the stream was increasing.

Cmdr Hadfield's son Evan told The Register that he wasn't worried about any danger to the ISS crew.

"Although this is unexpected, Dad is not unprepared. Only when a problem occurs that he is not prepared for will I feel truly nervous. Right now it is a car full of mechanics that is leaking a bit of oil. I have absolute faith in their ability to fix it," he said.

However, Vladimir Solovyov, flight director for the Russian side of the orbiting science lab, was slightly more stern. "They have a serious defect, very serious," Solovyov told the Interfax news agency.

The ammonia loop is the same one that spacewalkers already tried to fix during an outing last November, although NASA doesn't know if the leak is from the same spot in the complex system.

Now crew members Chris Cassidy and Tom Marshburn, who have both spacewalked before, are getting ready to head out the airlock to help engineers figure out where the ammonia is streaming from.

Cmdr Hadfield, known for tweeting pics of Earth and recording music in space among other talents, was in good spirits this morning despite the leak. He declared:

NASA said that the crew are in no danger and the US space agency has already managed to reconfigure the station's power systems to transfer the electrical load before the coolant runs out.

Evan said Cmdr Hadfield was understandably "a bit busy right now" but the crew onboard and on the ground were "among the most capable humans on the planet" and there was no one he trusted more to sort the leak out.

There has been no word yet on whether Hadfield, Marshburn and Russian cosmonaut Roman Ramanenko can head home on Monday as planned. ®